1. Field of the Invention
The present invention relates to the structure of a dichoric filter and a method of making the same to provide color encoded signals for video transmission.
2. Description of the Prior Art
In the evolution of color video transmission, various forms of filters and complementary electrical circuits have been utilized to produce a plurality of video signals for subsequent transmission and reconstruction as a projected image. Generally, color television cameras have utilized a single scanning beam with a complementary optical system for focussing the light from the photographic object onto a photoelectric surface to optimize the derivation of a frequency electrical signal representative of component colors and intensity variations. The derivation of a sharp and definitive color signal free of noise or interference has been a prime object in the prior art. In addition, the optical generation of video signals representing both color and brightness which can be easily isolated for subsequent processing has been another goal of the prior art.
Typically, the light from a photographic object is optically converted by a filter into component colors for application to a photoelectric surface of a vidicon or image tube. The scanning beam of the tube will scan the raster to produce a plurality of signal carriers that are respectively amplitude modulated in accordance with the intensity variations of the respective selected component color. The use of a parallel striped filter in such a system is well known as disclosed in the Kell U.S. Pat. No. 2,733,201 and Lesti U.S. Pat. No. 3,378,633 wherein an encoding filter is provided with two grids of lines which have different substractive primary colors and which are angularly superimposed upon one another.
Another example of an encoding filter is found in the Thomasson et al U.S. Pat. No. 3,771,857 wherein a multi layer striped filter is produced with a photo resist technique. The Larsen et al U.S. Pat. No. 3,681,519; Shinosaki U.S. Pat. No. 3,860,955 and Hasegawa U.S. Pat. No. 3,875,627 are cited of general interest. While numerous encoding filters have been utilized in video transmission there still exists problems in providing efficiently manufactured filters that solve the problems of incorporating an optical filter into an electrical scanning system. In particular, there is still a demand to minimize the optical refracting problems and electrical charge problems that are capable of diminishing the integrity of the resulting encoded signals.